If it's not the IAC or TPS...what could it be?

[GearheadJLM]

Vehicle: 2004 Ranger XLT 4x4 4.0L SOHC Ext Cab Step side 5 speed w/129k

What's done to it: Flowmaster Catback, K&N Air Filter

No Check Engine Light (CEL)

Here's the issue: Say I am cruising or just trying to shift and the RPM is at about 1800-2200, When I push in the clutch (and let off the gas) the RPM's will jump up to around 3200 and hold for about 2 seconds, then drop to around 2500 for a second or so, then 1500 and then finally down to 800-900 (by this time I'm stopped). Speed, engine temp, and outside temp seem to have no effect on it.

I have tried to replace the IAC and TPS. I tried taking the Mass Airflow Sensor out and cleaning it with rubbing alcohol. I put new plugs in, and it didn't make a difference.

I am questioning EGR Valve, but am most expecting a hard to find vacuum leak. I tried spraying Ether (starting fluid) around vacuum lines and intake to see if I noticed a difference, and didn't.

Has anybody else had this issue? What else could it be? How else can I diagnose and find a vacuum leak?

Any help would be appreciated.

Here's some pics:

 

[wyochimneysweep]

pvc vavle sticking can cuz more air to enter the engine.

 

[mudbug0426]

you said the check engine light was not on, but did you scan to see if there are any pending codes on the computer?

 

[GearheadJLM]

you said the check engine light was not on, but did you scan to see if there are any pending codes on the computer?

This is a negative.

 

[mudbug0426]

if you have a scanner tool, scan the computer, if not take it to autozone and have them see if there are any pending codes on the computer. most of the time pending codes will not make the check engine light come on

 

[GearheadJLM]

Problem solved.

Technical Service Bulletin 05510 - High Idle Between Shifts

Cure: Had the ECU reprogrammed by dealer... Cost me $80